Osteodistraction or distraction osteogenesis is the process by which the slow, incremental distraction of fracture callus is used to stimulate and prolong active bone formation, thereby providing a means of bridging what would otherwise be a large bony defect. Distraction osteogenesis is used in the reconstruction of skeletal deformities and the lengthening of bones, such as in the treatment of pediatric limb length inequality.
In osteodistraction procedures, the bone is surgically split in two segments, and the two ends of the bone are gradually moved apart (distraction phase). The rate at which the two bone segments are moved apart is slow enough so that new bone can form in the gap. When the desired length has been reached, a consolidation phase follows.
Whether in the long bones or in the craniofacial skeleton, distraction osteogenesis takes place primarily through intramembranous ossification. Histologic studies have identified 4 stages that result in the eventual formation of mature bone.
Stage I: The intervening gap initially is composed of fibrous tissue (longitudinally oriented collagen with spindle-shaped fibroblasts within a mesenchymal matrix of undifferentiated cells).
Stage II: Slender trabeculae of bone are observed extending from the bony edges. Early bone formation advances along collagen fibers with osteoblasts on the surface of these early bony spicules laying down bone matrix. Histochemically, significantly increased levels of alkaline phosphatase, pyruvic acid, and lactic acid are noted.
Stage III: Remodeling begins with advancing zones of bone apposition and resorption and an increase in the number of osteoclasts.
Stage IV: Early compact cortical bone is formed adjacent to the mature bone of the sectioned bone ends, with increasingly less longitudinally oriented bony spicules; this resembles the normal architecture.
Bone remodeling begins during the consolidation phase and continues over 1-2 years, eventually transforming the regenerated bone into a mature osseous structure similar in size and shape to the adjacent bone. Although the volume of new bone is comparable to that of adjacent bones, animal studies show that mineral content and radiodensity is approximately 30% less, as is the tensile strength of the regenerated segment.
Moreover, delayed consolidation following distraction is a troubling complication. When delayed consolidation occurs, removal of bone fixators is postponed and the risk of other complications, such as infection, is increased.
In view of the problems associated with consolidation and the resulting new bone structure, it would be desirable to provide alternative osteogenic regeneration systems for use in osteodistraction procedures. It would additionally be desirable to provide methods of using alternative osteogenic regeneration systems in osteodistraction procedures.